1998 626 ES check engine light

I have a 98 626 with 192000 miles on it. The check engine light is on and the code was read to be P0400 - EGR flow malfunction. I have had this problem previously - at 96000 miles. At that time I was told I needed a new EGR valve. I had it installed but the problem did not go away. The dealer had to keep the car for close to 2 weeks and ultimately replaced the computer to get the light to stay off. The first time I had this problem the light came on, then went off for a period of time - then on again. Eventually it stays on constantly. The same thing happened this time around. I am skeptical about replacing the EGR valve because it didn't solve anything the first time. I have seen suggestions ranging from replacing the O2 sensors to cleaning the existing EGR valve to not topping off the tank when filling with gas. The car does not run choppy or rough. The kicker is that with the light on it will not pass an emissions test.

Any suggestions would be welcomed.